Inhibition of corrosion in wells



Patented Nov. 16, 1948 INHIBITION OF CORROSION IN WELLS Prentiss S. Viles and Elza Q. Camp, Goose Creek, Tex., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application January 24, 194.6, Serial No. 643,206

4 Claims.

The present invention is directed to the pro-- duction of fluids from underground formations.

More particularly, the invention is directed to protecting the conduits and attendant eqinpment, through which fluids from subsurface formations are flowed and processed, from corrosion by materials occurring in or are introduced into fluids originating in subsurface formations.

In many oil, gas, and condensate fields, the production of fluids from subsurface formations is accompanied by extremely severe corrosion of the conduits and attendant equipment which comes into contact with the fluid mixture being produced. In many cases it is found that the fluid mixture is acidic innature and comprises substantial amounts of carbon dioxide, a portion of which dissolves in water present to form carbonic acid. In addition to the carbon dioxide other materials which are present in the corrosive mixture may include organicacids, inorganic acids, inorganic salts and acidic sulfur compounds. These corrosive substances occur in or are introduced into the fluids originating in the subsurface formations. In some cases the corrosion occurs throughout the conduits and attendant equipment through which the fluids from the subsurface formations are flowed and processed. In other cases the corrosion is limited primarily to portions of the conduits near the surface of the wells and to the wellhead and attendant equipment. In all cases it has been necessary to make extensive replacements of equipment that has failed as a result of corrosion. This not only limits production, but is extremely expensive, particularly in those cases in which it is necessary to kill a high pressure well in order to make repairs and. to replace corrodedequipment. In addition to the high costs of making repairs to well equipment, there is a marked loss in revenues due to having a well off production and to the necessity of having to maintain additional wells and sources of supply to meet production requirements during periods in which a well is off production for repairs as a result of corrosion. Further, there is constant danger that a well will flow wild as a result of the failure of equipment due to corrosion. In cases of this kind, enormous losses are incurred. It is, therefore. the main object of the present invention to provide a method whereby corrosion is substantially eliminated or inhibited in the conduits and attendant equipment through which fluids from subsurface formations are flowed and processed.

In accordance with the present invention, cor.

2 rosion of ferrous metal surfaces is inhibited or substantially eliminated by adding to fluid mixtures produced from subsurface formations and which are acidic in nature and include carbon dioxide a small amount of carbon disulfide. The amount of carbon disulfide employed to inhibit the corrosion of the ferrous metallic surfaces by the fluid mixtures may-be varied over a wide range and satisfactory results obtained. Inasmuch as sulfur-containing compounds are usually undesirable constituents in the hydrocarbon fluid being obtained, it is preferable to employ only small amounts of carbon disulfide to inhibit the corrosion but in some cases relatively large amounts of the carbon disulfide may be desirable or necessary and in such instances it may be added in amounts up to 3% by weight based on the weight of fluid mixture produced from the subsurface formation. However, it will usually be found that minor amounts of carbon, disulfide will be eifective for inhibiting corrosion of the ferrous metal surfaces and, accordingly, under many operation conditions carbon disulfide used for eifectively inhibiting corrosion may be .1% or even as low as .01% by weight of the fluid mixture being produced.

It may be found that after an effective amount of carbon disulfide has been employed to inhibit corrosion of the ferrous metal surface, a lower amount may be effective thereafter to maintain the inhibiting effect. Accordingly, a substantial amount of carbon disulfide, as of the order of 1% by weight of the fluid produced, may be employed for an interval of time sufiicient to cause corrosion of the metallic surfaces to be eifectively inhibited and thereafter smaller amounts, as of the order of .01% of carbon disulfide based on the weight of the fluid produced. may be employd to maintain the inhibited condition of the metallic surfaces.

It will be found convenient to suspend or dissolve the carbon disulfide in a suitable vehicle before introducing it into the fluid mixture. The resultant suspension or solution may then be conveniently injected 'into the borehole adjacent the subsurface formation from which the fluid is produced or maybe introduced into the conduit through which the fluid mixture flows from a subsurface formation to the surface of the earth. Another method of employing the inhibiting agent is by injecting the suspension or solution into the subsurface reservoir by employing an adjacent well; it will be apparent that when adding the inhibiting agent in accordance,

Withthis procedure the fluid entering the borehole of the producing well will comprise the inhibiting agent.

An advantage of the process of the present invention, irrespective of the suppression of corrosion of the conduits and attendant equipment through which fluids from subsurface formations are flowed and processed, is the ability to operate without interruptions due to failure of equipment. The danger of a well flowing wild is minimized and the necessity of having a surplus of wells to insure production is eliminated.

In order to illustrate further the beneficial effects of the present invention, the following examples are given:

EXAMPLE I peratures and pressures at which the tests were conducted. One of the solutions was employed as a blank with no inhibiting material added while the other solution had carbon disulflde added thereto. The results obtained by the test are shown in Table I.

Table I Reduction of Corrosion by Inhibition, Per Cent Corrosion Material, Per Cent by Wt. pa

Inhibiting Material None None 0.2250 Carbon Dlsulilde 1.0 0.0269

In order to determine the effectiveness of alternating the pressure on the inhibiting agent. a series of tests was conducted as follows:

Exam: II

A quantity of distilled water was divided into a plurality of samples. Some of the samples were maintained as distilled water; to other of the samples acetic acid was added to obtain a pH of 4.5; to other samples of distilled water hydrochloric acid was added to obtain a pH of 4.5; in other samples a low concentration of sodium chloride was dissolved, while to still other samples a high concentration of sodium chloride was dissolved. Some of the samples were then inhibited by adding CS2 thereto. Test pieces of carbon steel were immersed in the solutions prepared. One set of samples was then maintained under the pressure of 100 lbs. per sq. in. gauge of carbon dioxide, a second set of samples was maintained under a pressure of 500 lbs. per sq. in. gauge of carbon dioxide while a third set of the samples was maintained under a pressure of 900 lbs. per sq. in. gauge of carbon dioxide. In conducting the tests the sets of samples were maintained under superatmospheric pressure for an intervai'tof 24 hours and at a temperature of 170 F. The results obtained when conducting the tests under a pressure of 100 lbs. per sq. in. are set forth in Table II below; the results obtained when conducting the tests under a pressure of 500 lbs. per sq. in. are shown in Table III below, while the results obtained when conducting the tests under a pressure of 900 lbs. per sq. in. are shown in Table IV below.

Table II Corrosion Rate, Inch Per Year ltductgm in orro on Type Inhibited Rate, Per- Without With 1 Wt. cent Inhibitor Percent of CS:

Distilled Water 0. 2250 0. 0269 88. 0 Distilled Water Adjusted to pH 4.5 with Acetic Acid 0. 1869 0. 0175 90. 7 Distilled Water Adjusted to pH 4.5 with Hydrochloric Acid 0. 0555 0. 0166 71. 0 Water of Low Salt Content... 0. 1189 0. 0209 82. 0 Water 0! High Bait Content..- 0. 1098 0. 0197 82. 0

Table III Corrosion Rate, Inch Per Year Reduction in orros on Inhibited Rate, Per- Without With 1 Wt. 9 cent. Inhibitor Percent of CS:

. Distilled Water 0. 2083 0. 0278 86.3

Distilled Water Adjusted to EH 4.5 with Acetic Add... 0. 1070 0. 0164 '86. 0 D tilled Water Adjusted to pH 4.5 with Hydrochloric Acid 0. 0343 Water 01 Low Salt Content..- 0. 1073 0. 0189 82. 0 Water of High Salt Conten 0.0447

Table IV Corrosion Rate, Inch Per Year Rductlim in 1 arms on i Inhibited Rate, Per- Without With 1 Wt. cent Inhibitor Percent of CS:

Distilled Water 0. 2100 0. 0219 89. 5 Distilled Water Adjusted to H 4.5 with Acetic Acid. 0. 1060 0. 0401 62. 3 D stilied Water Adjusted to pH 4.5 with Hydrochloric Acid 0. 0310 Water of Low Salt Content... 0.1307 0. 0179 86. 3 Water of High Salt Content 0. 0182 It will be observed from the data presented above that the addition of a small amount of carbon disulflde effects a marked reduction in the tendency of a corrosive water solution to corrode carbon steel. It is to be noted that all sulfur-containing compounds are not effective for inhibiting corrosion of ferrous metallic surfaces when exposed to corrosive fluids produced from subsurface formations. For example, ethyl sulfate is entirely ineifective in inhibiting the corrosion of ferrous metallic surfaces by such fluids.

The nature and objects of the present inventicn having been fully described and illustrated. what we wish to claim as new and useful and to secure by Letters Patent is:

1. A method for reducing the corrosiveness to corrodible ferrous metal of a corrosive petroliferous' weli fluid including moisture and carbon dioxide which comprises introducing into said fluid a. corrosiori inhibiting amount of carbon 3. A method in accordance with claim 1 in UNITED STATES PATENTS which the carbon disulflde is introduced into the corrosive fluid in a subsurface formation at a Number Name Date point remote from the point at which the fluid .82 .7 Walker Oct. 27, 1931 is produced. 5 1, 4,8 De Groote Feb. 9, 1932 4. A method in accordance with claim 1 in 1, 73, 4 Walker Aug. 23, 1932 which the corrosive fluid is produced from a sub- 2, 7,5 9 Smith Sept. 5, 1944 surface formation through a iermus metal con- THER duit and in which the carbon disulflde is intro- 0 REFERENCE-S duced directly into said conduit 10 Formaldehyde vs. Sulfide Corrosion, article in PRENTISS s 11 5, Industrial and Engineering Chemistry, Industrial ELZA Q. CAMP. edition, vol. 38, pages 10 and 1d.

REFERENCES CITED The following references are of record in the 15 file of this patent: 

